Tool, tool holder, and machine tool

ABSTRACT

A tool attachable to a spindle of a machine tool in the same way as an ordinary tool, capable of being driven without connecting with an external power supply etc., giving a higher rotational speed than that of the spindle of the machine tool without supplying electric power from the outside, and able to be changed automatically, provided with a machining tool for machining a workpiece, a motor for driving the machining tool, a generator for generating electric power to drive the motor by the rotation of the spindle, and a rotational speed detecting device for detecting the rotational speed of the motor based on a received light signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application of U.S. application Ser. No.10/949,342, filed Sep. 27, 2004, now U.S. Pat. No. 7,052,219, which is aDivisional of U.S. application Ser. No. 10/268,987, filed Oct. 11, 2002,now U.S. Pat. No. 6,808,345, which is based upon and claims the benefitof priority from the prior Japanese Patent Application Nos. 2001-318339,filed Oct. 16, 2001, 2001-356506, filed Nov. 21, 2001, and 2001-357577,filed Nov. 22, 2001, the entire contents all of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tool to be attached to a spindle of amachine tool for machining a workpiece.

2. Description of Related Art

In for example a machining center or other machine tool provided with aspindle, the maximum rotational speed of the spindle is determined bythe structure of a main bearing rotatably supporting the spindle and alubrication system of this bearing. For this reason, when it isnecessary to rotate a tool at a higher rotational speed than the maximumrotational speed of the spindle, an accelerating apparatus is used.

As the accelerating apparatus, for example, an accelerating apparatusprovided with a gear mechanism such as epicyclic gearing which holds thetool and is removably attachable to the spindle is well known.

For example, in a machining center, when it is desired to increase therotational speed of the tool to higher than the maximum speed of thespindle temporarily, an accelerating apparatus such as the aboveaccelerating apparatus is attached to the spindle in the same way as anordinary tool to enable the tool to be rotated at a higher rotationalspeed.

However, when raising the rotational speed of the tool to a higher speedthan the maximum rotational speed of the spindle by the above gearmechanism, the accelerating apparatus increasingly generates heat at asuper high rotational speed such as tens of thousands to hundreds ofthousands of revolutions per minute, so the machining tolerance of aworkpiece can be influenced by the heat. Further, at the above superhigh rotational speed, the noise from the accelerating apparatus canalso increase. Furthermore, a highly reliable precision structure ableto withstand the above super high rotational speed is required for theaccelerating apparatus, so there is the disadvantage that themanufacturing cost becomes relatively high.

Further, in a case of an accelerating apparatus with a gear mechanism,it is needed to lubricate the gear or bearing and arrange a supplypassage and a discharge passage for the lubricating oil in theaccelerating apparatus, so there is the disadvantage that the apparatusbecomes larger and it is difficult to automatically change the tool byan automatic tool changer.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a tool and a toolholder to be removably attached to a spindle of a machine tool in thesame way as an ordinary tool, capable of operating without connecting anexternal power supply etc., giving a higher rotational speed than thatof the spindle of the machine tool, and automatically changing a tool.

Another object of the present invention is to provide a machine toolprovided with the above tool and tool holder.

According to a first aspect of the present invention, there is provideda tool attachable to a spindle of a machine tool comprising a machiningtool for machining a workpiece; a motor for driving the machining tool;a generator for generating electric power to drive the motor by therotation of the spindle; and a breaking means for breaking a supply lineof electric current from the generator to the motor when electriccurrent over a predetermined value flows in the supply line.

According to a second aspect of the present invention, there is provideda tool attachable to a spindle of a machine tool comprising a machiningtool for machining a workpiece; a motor for driving the machining tool;a generator for generating electric power to drive the motor by therotation of the spindle; a control means for controlling a supply ofelectric power generated by the generator to drive and control themachining tool; and a driving state detecting means for detecting thestate of the motor; wherein the control means drives and controls themotor based on the information detected by the driving state means.

According to a third aspect of the present invention, there is provideda tool attachable to a spindle of a machine tool comprising a machiningtool for machining a workpiece; a motor for driving the machining tool;a generator for generating electric power to drive the motor by therotation of the spindle; a light signal generation means for generatinglight signal in accordance with the rotational speed of the motor; and alight guiding means for guiding light into the light signal generationmeans from outside to output the light signal by the light signalgeneration means to the outside.

According to a fourth aspect of the present invention, there is provideda tool attachable to a spindle of a machine tool comprising a machiningtool for machining a workpiece; a motor for driving the machining tool;a generator for generating electric power to drive the motor by therotation of the spindle; a rotational speed detecting means fordetecting the rotational speed of the motor; and a rotational speeddisplaying means for displaying the rotational speed detected by therotational speed detecting means so as to be visually recognized fromthe outside.

In the first aspect of the present invention, the tool attachable to thespindle is provided with a generator and a motor, generates electricpower using the rotation of the spindle, drives the motor with thegenerated electric power, and rotates the cutting tool. By this, itbecomes possible to drive the tool without connecting with the externalpower supply, etc. and also change automatically the tool.

Further, the tool of the present invention generates electric powerusing the rotation of the spindle. Due to this, even when the cuttingtool is overloaded while machining, the spindle is driven continuously.So, there is a possibility that the excessive current flows in thegenerator or the. Accordingly, in the present invention, if the currentover predetermined value flows the supply line from the generator to themotor, the generator and the motor are protected by breaking the supplyline.

In the second aspect of the present invention, the driving state of themotor is detected by the driving state detecting means and is fed backto the control means to control the motor. By this, it becomes possibleto control the tool independently of the spindle, variously andprecisely.

In the third aspect of the present invention, the tool is provided witha light signal generating means and a light guiding means and generateslight signal in response to the rotational speed of the motor by thelight generating means using light input from outside, and outputs thelight signal to outside. By detecting the rotational speed of the motorbased on the output light signal, a light source or a light receivingdevice is not necessarily built in the tool and it becomes possible tomake the tool compact.

In the fourth aspect of the present invention, the tool attached to thespindle is provided with a generator and a motor, generates electricpower by the rotation of the spindle, and drives the motor with thegenerated electric power to rotate the cutting tool. When the motorrotates, the rotational speed is detected by the rotational speeddetecting means and is displayed visually recognizably by the rotationalspeed display means. Due to this, it is possible to grasp easily thedriving state of the tool.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore apparent from the following description of the preferredembodiments given in relation to the accompanying drawings, wherein:

FIG. 1 is a view of the configuration of a machining center as anexample of a machine tool according to the present invention;

FIG. 2 is a sectional view of a tool according to the first embodimentof the present invention;

FIG. 3 is a view of the connection state of a motor and generator;

FIG. 4 is a view of the connection state of a motor and generator in atool according to a second embodiment of the present invention;

FIG. 5 is a view of the appearance of a tool according to a secondembodiment of the present invention;

FIG. 6 is a view of the connection state of a motor and generator in atool according to a third embodiment of the present invention;

FIG. 7 is a view of the configuration of a tool according to a fourthembodiment of the present invention;

FIG. 8 is a view of a main configuration for detecting the rotationalspeed of a motor;

FIG. 9 is a view of the configuration of a tool according to a fifthembodiment of the present invention; and

FIG. 10 is a view of the configuration of an electrical system of a toolaccording to a fifth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The tool of the present invention generates electric power using therotation of the spindle. Due to this, even when the cutting tool isoverloaded while machining, the spindle is driven continuously.Therefore, there is a possibility of an excessive current flowing in thegenerator or the motor. Accordingly, in the present invention, if acurrent over a predetermined value flows through the supply line fromthe generator to the motor, the generator and the motor are protected bybreaking the supply line.

Also, the driving state of the motor is detected by the driving statedetecting means and is fed back to the control means to control themotor. By this, it becomes possible to control the tool independently ofthe spindle, variously, and precisely.

Further, the tool is provided with a light signal generating means and alight guiding means, generates a light signal in response to therotational speed of the motor by the light generating means using lightinput from outside, and outputs the light signal to the outside. Bydetecting the rotational speed of the motor based on the output lightsignal, no light source or light receiving device need be built in thetool and it becomes possible to make the tool more compact.

The tool attached to the spindle is provided with a generator and amotor, generates electric power by the rotation of the spindle, anddrives the motor with the generated electric power to rotate the cuttingtool. When the motor rotates, the rotational speed is detected by therotational speed detecting means and is displayed visually recognizablyby a rotational speed display means. Due to this, it is possible toeasily grasp the driving state of the tool.

Below, an explanation will be made of embodiments of the presentinvention by referring to the drawings.

First Embodiment

FIG. 1 is a view of the configuration of a machining center as anexample of a machine tool according to the present invention. Note thatthe machining center is a numerical control machine tool capable ofso-called combined machining.

The machining center 1 is provided with a machine tool body 2, anumerical control apparatus (NC apparatus) 250, and a programmable logiccontroller (PLC) 150.

In FIG. 1, the machine tool body 2 is provided with a cross rail 37having two ends movably supported by shafts of a double housing typecolumn 38. A ram 45 is provided movably in a vertical direction (Z-axisdirection) via a saddle 44 supported movably on this cross rail 37.

The saddle 44 is provided with a not illustrated nut part passingthrough the cross rail 37 in a horizontal direction. A feed shaft 41with a screw part formed on the outer circumference is screwed into thisnut part.

A servo motor 19 is connected with an end of the feed shaft 41. The feedshaft 41 is driven to rotate by the servo motor 19.

By the rotation of the feed shaft 41, the saddle 44 moves in the Y-axisdirection. By this, the ram 45 is moved and positioned in the Y-axisdirection.

Further, the saddle 44 is provided with a not illustrated nut part inthe vertical direction. The feed shaft 42 with a screw part formed onthe outer circumference is screwed into this nut part. A servo motor 20is connected with an end of the shaft 42.

The servo motor 20 drives the feed shaft 42 to rotate. By this, the ram45 movably provided on the saddle 44 is moved and positioned in theZ-axis direction.

The ram 45 has built into it a spindle motor 31. This spindle motor 31rotates a spindle 46 rotatably supported by the ram 45. A tool T such asan end mill is attached at the front end of the spindle 46. The tool isdriven by the rotation of the spindle 46.

Below the ram 45, a table 35 is provided movably in the X-axisdirection. The table 35 is provided with a not illustrated nut part. Anot illustrated nut feed shaft provided along the X-axis direction isscrewed into this nut part. This not illustrated feed shaft is connectedto the servo motor 18.

The table 35 is moved and positioned in the X-axis direction by therotation and driving of the servo motor 18.

Further, the double housing column 38 is provided with a not illustratednut part. The cross rail 37 is raised and lowered by the rotation of thefeed shaft 32 a screwed into it by a cross rail elevation servo motor32.

An automatic tool changer (ATC) 39 automatically changes the tool Tattached to the spindle 46.

That is, the automatic tool changer 39 holds various tools in its notillustrated magazine, returns a tool T attached to the spindle by a notillustrated tool changing arm into the magazine, and attaches a requiredtool held by the magazine to the spindle by the tool changing arm.

The NC apparatus 250 drives and controls the above servo motors 18, 19,and 20, and the cross rail elevation servo motor 32.

Specifically, the NC apparatus 250 controls the positions and the speedsbetween a workpiece and the tool T by the servo motors 18, 19, and 20according to a machining process defined in advance in a machiningprogram. Further, the NC apparatus 250 controls the rotational speed ofthe spindle 46 by decoding the rotational speed of the spindle 46defined by an S-code in the machining program.

Still further, the NC apparatus 250 automatically changes various toolsby decoding the tool changing operation of the tool T defined by forexample an M-code in the machining program.

The PLC 150 is connected to the NC apparatus 250 and the operationalpanel 200. The PLC 150 performs various kinds of sequence control forexample starting and stopping the machining center 1 in accordance witha predetermined sequence program, outputting signals to switch on andoff the display part of the operational panel 200, etc. Further, the PLC150 is connected to a spindle motor driver 157 to drive and control thespindle motor 31. The PLC 150 outputs control commands to start and stopthe spindle motor 31 and control its speed to the spindle motor driver157.

FIG. 2 is a sectional view of a tool according to the first embodimentof the present invention.

In FIG. 2, a tool 60 is comprised of a cutting tool 100 and a toolholder 61. Note that the cutting tool 100 is an embodiment of amachining tool according to the present invention. Further, the tool 60according to the present embodiment is attached to the spindle 46 by theautomatic tool changer 39 in the same way as the above ordinary tool T.

The tool holder 61 has an attachment part 62, a casing 65 comprised ofcasing parts 66, 67, and 68, a generator 70, a motor 80, a tool holdingpart 90, and a locking part 85.

The attachment part 62 is provided with a grip 62 a, a taper shank 62 bto be attached to a taper sleeve 46 a formed at the front end of theabove spindle 46, a pull stud 62 c formed at the front end of this tapershank 62 b, and a shaft 62 d rotatably held by the casing part 66.

The grip 62 a of the attachment part 62 is gripped by the above toolchanging arm of the automatic tool changer 39 when the tool 60 is beingattached to the spindle 46 from the magazine of the automatic toolchanger 39 and when the tool 60 is being conveyed from the spindle tothe magazine of the automatic tool changer 39.

The center of the taper shank 62 b of the attachment part 62 becomesconcentric with the center of the spindle 46 by being attached to thetaper sleeve 46 a of the spindle 46.

The pull stud 62 c of the attachment part 62 is clamped by a collet of anot illustrated clamping mechanism built in the spindle 46 when theattachment part 62 is attached to the taper sleeve 46 a of the spindle46. Note that the clamping mechanism built in the spindle 46 is wellknown, so a detailed explanation will be omitted.

The shaft 62 d of the attachment part 62 is supported rotatably held bythe inner circumference of the casing part 66 via a plurality ofbearings 72. As the bearing 72, a sealed ball bearing can be used.

The sealed ball bearing is called a capped bearing in the JIS (JapanIndustrial Standard) or the ISO (International Standard Organization).

A sealed ball bearing is for example a bearing where grease is sealedinto a space enclosed by sealing parts arranged at the two sides of aninner ring and an outer ring.

By using such a sealed ball bearing, it is not necessary to formpassages for supply and discharge of lubricating oil in the tool 60 andit becomes possible to make the tool 60 more compact.

The generator 70 and the motor 80 are held by the inner circumference ofthe casing part 67 via a holding part 73.

The shaft 62 d of the attachment part 62 is connected with the inputshaft 71 of the generator 70. As this generator 70, for example, athree-phase synchronous generator can be used.

As shown in FIG. 3, the motor 80 is connected to the generator 70 withthree conductor cables CU, CV, and CW. The electric power generated bythe generator 70 is supplied to the motor 80. The motor is driven by theelectric power supplied from the generator 70.

As this motor 80, for example, a three-phase induction motor can beused.

Fuses FU, FV, and FW are respectively arranged at the middles of theabove conductor cables CU, CV, and CW.

The fuses FU, FV, and FW are arranged at predetermined locations in theabove casing 60.

These fuses FU, FV, and FW break the circuit between the motor 80 andthe generator 70 for example by melting when current over apredetermined value flows in the conductor cables CU, CV, and CW. Bythis, it becomes possible to avoid damage by heat caused by excessivecurrent in the generator 70 and the motor 80.

As the fuse Fu, FV, or FW, for example, a member comprised of analuminum, zinc, copper, or other member accommodated in a cylinder madeof glass or fiber can be used.

In FIG. 2, the tool holding part 90 has a shaft 91, a coupling 93 forconnecting this shaft 91 and the output shaft 81 of the motor 80, and atool attachment part 95. Note that the shaft 91 and the shaft 81 areembodiments of a driving shaft according to the present invention.

The shaft 81 of the motor 80 is rotatably held by a not shown bearing.As the bearing, a sealed ball bearing can be used.

The shaft 91 is rotatably held by the inner circumference of the casingpart 68 via a plurality of bearings 92. As the bearings 92, sealed ballbearings can be used.

The shaft 91 is stopped by a stopper 94 at the casing part 68 at itsfront end side.

The cutting tool 100 is held by the tool attachment part 95. Thiscutting tool 100 machines a workpiece. Note that the tool attachmentpart 95 is an embodiment of the tool attachment part according to thepresent invention.

Specifically, as the cutting tool 100, a cutting tool such as a drill oran end mill may be used.

The casing parts 66, 67, and 68 are connected to each other by clampingmeans such as bolts. The casing 65 is constructed by these casing parts66, 67, and 68.

The locking part 85 is mounted on the outer circumference of the casingpart 66.

When the attachment part 62 is attached to the taper sleeve 46 a of thespindle 46, the front end of the locking part 85 is inserted to anengagement hole 47 a formed at a non-rotating part such as the ram 45 onthe spindle 46 side.

Due to this, even if the spindle 46 is rotated, rotation of the casing65 is prevented.

Next, an explanation will be made of an example of the operation of theabove configured tool 60.

First, the automatic tool changer 39 attaches the tool holder 61 holdingthe cutting tool 100 at the tool attachment part holder 95 to thespindle 46 of the machining center 1. The front end 85 a of the lockingpart 85 is inserted into the engagement hole 47 a of the non-rotatingpart 47 whereby the rotation of the casing 65 is prevented.

By rotating the spindle 46 at the rotational speed N₀ from this state,the attachment part 62 of the tool holder 61 is rotated and the rotationof the spindle 46 is transmitted to the generator 70. By this, thegenerator 70 generates electric power. In the case of a three-phasesynchronous generator used as the generator 70, the generator 70generates three-phase alternating current.

The frequency F of the three-phase alternating current generated by thegenerator 70 is expressed by the following formula (1) where the numberof poles of the generator 70 is p₁ and the rotational speed of thespindle 46 is N₀ [min⁻¹]:F=p ₁ *N ₀/120 [Hz]  (1)

Accordingly, when the spindle 46 is rotated at the rotational speed N₀,a three-phase alternating current having the frequency F expressed theabove formula (1) is supplied to the motor 80.

Here, in case where a three-phase induction motor is used as the motor80, if the number of poles of the motor 80 is p₂, the motor 80 isrotated by 2/p₂ per cycle of the three-phase alternating current.

Therefore, the synchronous rotational speed of the motor 80 is expressedby the following formula (2):N ₁=120*F/p ₂ [min⁻¹]  (2)

Accordingly, the relationship of the rotational speed N₁ of the cuttingtool 100 to the rotational speed N₀ of the spindle 46 is expressed bythe following formula (3):N ₁ =N ₀ *p ₁ /p ₂ [min⁻¹]  (3)

As understood from formula (3), the rotational speed N₀ of the spindle46 is changed to the rotational speed N₁ expressed by the above formula(3).

As expressed by the formula (3), it is found that by appropriatelysetting the ratio between the number of poles p₁ of the generator 70 andthe number of poles p₂ of the motor 80, it is possible to freely set theratio of the rotational speed of the cutting tool 100 to the rotationalspeed of the spindle 46.

That is, when trying to raise the rotational speed of the cutting tool100 higher than that of the spindle 46, the ratio of the number of polesp₁/p₂ is set larger than 1. When trying to reduce the rotational speedof the cutting tool 100 to lower than that of the spindle 46, the ratioof the number of poles p₁/p₂ is set smaller than 1.

When machining a workpiece such as aluminum alloy, sometimes therotational speed of the cutting tool 100 is raised higher than themaximum rotational speed of the spindle 46.

In such a case, the tool 60 is held in advance in the magazine of theautomatic tool changer 39 of the machining center 1.

For example, when the maximum rotational speed Nmax of the spindle 46 ofthe above machining center 1 is 3000 [min⁻¹] and the rotational speed ofthe cutting tool 100 is raised to 30,000 [min⁻¹], the generator 70 andthe motor 80 having a ratio of the number of poles p₁/p₂ of 10 are used.

The automatic tool changer 39 attaches the tool 60 automatically to thespindle 46 in the same way as an ordinary tool. Note that an ordinarytool is a cutting tool clamped by a tool holder.

The rotational speed of the cutting tool 100 held by the tool holder 61is controlled by the rotational speed of the spindle 46. Specifically,in the machining program downloaded at the NC apparatus 250, therotational speed of the spindle 46 is designated in advance by an S-codein accordance with the rotational speed of the cutting tool 100 held bythe tool holder 61.

For example, when rotating the cutting tool 100 at the rotational speedof 30,000 [min⁻¹], the rotational speed of the spindle 46 is designatedas 3000 [min⁻¹] by the S-code in the machining program.

When the spindle 46 is rotated at the rotational speed of 3000 [min⁻¹],the generator 70 generates a three-phase alternating current having afrequency in accordance with the rotational speed of the spindle 46 andthe number of poles of the generator 70 and motor 80.

The motor 80 is driven by the three-phase alternating current suppliedfrom the generator 70, while the cutting tool 100 held by the toolholder 61 is rotated at the rotational speed of about 30,000 [min⁻¹].

In the above state where the rotational speed of the cutting tool 100 isincreased, the workpiece is cut by moving the workpiece fixed on thetable 35 relative to the cutting tool 100 (spindle 46) in accordancewith the machining program.

Due to this, it becomes possible to suitably cut a workpiece such as analuminum alloy.

In this way, according to the present embodiment, the rotational speedof the cutting tool 100 is raised by driving the motor 80 by theelectric power generated by the generator 70. Due to this, even if thespindle 46 is rotated at a high rotational speed, heat is notincreasingly generated such as in a gear apparatus, so a reduction ofthe machining tolerance due to the heat can be avoided.

Further, according to the present embodiment, it is possible to make theinertia of the motor 80 smaller than the inertia of the spindle 46.Therefore, it becomes possible to improve the response of the cuttingtool 100 compared with when directly rotating the spindle 46 at a higherrotational speed.

Further, according to the present embodiment, a tool 60 which increasesthe rotational speed of the spindle 46 can be attached to the spindle 46and be changed by the automatic tool changer 39 in the same way as anordinary tool. Therefore, it is possible to immediately respond to arequest for machining at a higher speed while machining within anordinary rotational speed.

Further, according to the present embodiment, the cutting tool 100 isdriven by the electric power generated by the rotation of the spindle46. Therefore, it is not necessary to supply a driving current from theoutside. As a result, a cable for supplying electric power is notneeded.

Further, according to the present embodiment, when the cutting tool 100is overloaded while machining, it is possible to prevent the excessivecurrent from flowing to the generator 70 and the motor 80 and toreliably avoid damage to the generator 70 and the motor 80 by heat.

Second Embodiment

FIG. 4 is a view of the connection state of a motor and generator in atool according to a second embodiment of the present invention. Notethat the rest of the configuration of the tool according to the presentembodiment is the same as in the above mentioned embodiment.

As shown in FIG. 4, in the present embodiment, a circuit breaker CB isarranged in the middle of the conductor cables CU, CV, and CW connectingthe generator 70 and the motor 80 and is provided with an operationalpart OS.

The circuit breaker CB breaks the circuit between the motor 80 and thegenerator 70 when current over a predetermined value flows in theconductor cables CU, CV, and CW.

The operational part OS is movable between a connecting position Pa toconnect a circuit and a breaking position Pb to break a circuit. Whenthe circuit breaker is broken, the operational part OS located at theconnecting position Pa is automatically moved to the breaking positionPb.

By operating the operational part OS from the breaking position Pb tothe connecting position Pa again, the circuit between the motor 80 andthe generator 70 are connected again.

FIG. 5 is a view of an example of the arrangement of the above circuitbreaker in the tool.

As shown in FIG. 5, the operational part OS of the circuit breaker CB isarranged on the casing 65 and is visually recognizable and operable fromthe outside through a window Wd.

For example, when the circuit breaker CB detects excessive current andthe operational part OS is moved to the breaking position Pb whilemachining, it is possible for an operator to visually recognize that thecircuit between the motor 80 and the generator 70 is broken due to anexcessive current.

Further, the operator can connect the circuit between the motor 80 andthe generator 70 again by operating the operational part OS from thebreaking position Pb to the connecting position Pb.

In this way, according to the present embodiment, besides being able toprotect the motor 80 and the generator 70 from excessive current, itbecomes possible to improve the ease of operation.

Third Embodiment

FIG. 6 is a functional block diagram of the electrical system of a toolaccording to the present embodiment. Note that the mechanical structureof the tool according to the present embodiment is the same as in theabove mentioned first embodiment.

As shown in FIG. 6, the tool according to the present embodiment isprovided with a converter 200, an inverter 210, and a control circuit230 in addition to the generator 70 and the motor 80. Note that theconverter 200, the inverter 210, and the control circuit 230 form anembodiment of the control means of the present invention. Further, asthe generator 70, a three-phase synchronous generator can be used. Asthe motor 80, a three-phase induction motor can be used. Further, theconverter 200, the inverter 210, and the control circuit 230 are housedin the above casing 65.

The converter 200 is connected to the generator 70 by conductor cablesU1, V1, W1 and is electrically connected to the inverter 210 byconductor cables Wx and Wy.

The inverter 210 is connected to the motor 80 by conductor cables U2,V2, and W2. The inverter 210 converts a direct current supplied from theconverter 200 into a three-phase alternating current and supplies adriving current to drive the motor 80 via the conductor cables U2, V2,and W2 in accordance with pulse width modulation (PWM) signal 230 sinput from the control circuit 230.

The control circuit 230 outputs the PWM signal 230 s for controlling thedriving current supplied from the inverter 210 to the motor 80 throughthe conductor cables U2, V2, and W2 to the inverter 210. The PWM signal230 s controls the turn-on width of current of the inverter 210. Thecurrent value signal 312 s of the current detector 312 detecting thedriving current supplied to the motor 80 and the position signal 260 sof the rotational position detector 260 attached to the motor 80 areinput to the control circuit 230. Note that the current detector 312 andthe rotational position detector 260 are an embodiment of the drivingstate detecting means of the present invention for detecting the stateof the motor 80.

The control circuit 230 generates the PWM signal 230 s for driving andcontrolling the motor 80 by using the current value signal 312 s of thecurrent detector 312 and the positional signal 260 s of the rotationalposition detector 260 and gives this to the inverter 210.

Next, an explanation will be made of an example of the operation of thetool 60 according to the present embodiment.

The generator 70, a three-phase synchronous generator, generates athree-phase alternating current to be supplied to the converter 200. Thefrequency F of the three-phase alternating electric power generated bythe generator 70 becomes a value in accordance with the rotational speedN₀ of the spindle 46.

The current converted to a direct current by the converter 200 issupplied to the inverter 210, is converted to a three-phase alternatingcurrent with a frequency F in accordance with the PWM signal 230 s fromthe control circuit 230, and is supplied to the motor 80.

By controlling the frequency F of the alternating current supplied tothe motor 80 by the control circuit 230, it becomes possible to variablycontrol the rotational speed N₁ of the motor 80, that is, the rotationalspeed of the cutting tool 100, and to independently set the rotationalspeed N₁ of the motor 80 with regard to the rotational speed N₀ of thespindle 46.

Control of Electric Motor

The control of the motor 80 by the control circuit 230 is open-loopcontrol for changing the electric power generated by the generator 70into a three-phase alternating current with a frequency F by theinverter 210 to drive the motor 80 at a rotational speed in accordancewith the frequency F.

Accordingly, if the load given to the cutting tool 100 (the motor 80) ischanged while machining a workpiece by moving the workpiece relative tothe cutting tool 100 in accordance with the machining program, there isa possibility that a uniform quality of machining will not be possible.

Due to this, in the present embodiment, the position signal 260 sshowing the rotational position of the motor 80, the current valuesignal 312 showing the driving current of the motor 80, or other drivingstate of the motor 80 is detected, this is fed back to the controlcircuit 230, and the motor 80 is controlled by using the position signal260 s and the current value signal 312 s.

The control circuit 230 can convert the position signal 260 s into theactual rotational speed of the motor 80 and use this information tocontrol the motor 80 so as to maintain it at the desirable speedindependently of a change of the load given to the cutting tool 100.

Further, the control circuit 230 can control the motor 80 using thecurrent value signal 312 s so as to keep the torque generated by themotor 80 constant independently of a change of the load given to thecutting tool 100.

According to the present embodiment, since the tool 60 is provided witha converter 200, inverter 210, and control circuit 230 for controllingthe supply of the electric power generated by the generator 70 to themotor 80 and provided with a rotational position detector 260, currentdetector 312, or other driving state detecting means for detecting therotational speed, the driving current, or other driving state of themotor 80, it becomes possible to control the motor precisely.

Note that the method of driving and controlling the motor 80 by thecontrol circuit 230 described in the above embodiment is only anexample. The present invention is not limited to the above driving andcontrolling method. It is possible to employ other different kinds ofdriving and controlling methods.

Further, in the above embodiment, a rotation position detector 260 andcurrent detector 312 were illustrated as the driving state detectingmeans of the motor 80, but the present invention can also be applied toa driving state detecting means such as a taco-generator for detectingthe rotational speed of the motor 80, a torque sensor for detecting thetorque related the shaft of the motor 80, or other sensor for detectingthe driving state of the motor 80.

Fourth Embodiment

FIG. 7 is a sectional view of an embodiment of a tool according to thepresent invention.

In FIG. 7, the tool 603 is comprised of a cutting tool 100 and a toolholder 613 for holding the cutting tool 100. Note that the samereferences are used for the same parts as in the tool according to thefirst embodiment in FIG. 7.

Rotation Detecting Mechanism

The above tool 603 is provided with an optical fiber 200 inserted in athrough hole 65 h formed in the casing 65 and a through hole 85 hcommunicated with the through hole 65 h and formed in the locking part85, an optical part 201 connected to one end of the optical fiber 200,an optical part 202 connected to the other end of the optical fiber 200,and a reflecting mirror 125 mounted on the shaft 91 of the motor 80.Note that the optical fiber 200 and the optical parts 201 and 202constitute an embodiment of the light guiding means according to thepresent invention. The reflecting mirror 125 is an embodiment of thelight signal generation means according to the present invention.

On the spindle 46 side, an optical part 251 arranged in the fitting hole47 a of the non-rotation portion 47, an optical fiber 250 connected tothe optical part at its one end and inserted into a through hole 47 hformed in the non-rotation portion 47, and a sensor amplifier 400connected to the other end of the optical fiber 250 are arranged. Notethat the optical part 251, the optical fiber 250, and the sensoramplifier 400 constitute an embodiment of a light receiving and emittingmeans according to the present invention.

FIG. 8 is a view of the main configuration for detecting the rotationalspeed of the motor 80.

In FIG. 8, The optical part 201 is fixed at a position facing the shaft91 of the motor 80. The optical part 201 outputs the light guided by theoptical fiber 200 to the shaft 91 and guides the light reflected fromthe shaft 91 to the optical fiber 200.

When the locking part 85 is fit with the fitting hole 47 a of thenon-rotation portion 47, the optical part 202 is arranged facing theoptical part 251. The optical part 202 guides the light output from theoptical part 251 to the optical fiber 200 and outputs the lightreflected at the shaft 91 through the optical fiber 200 to the opticalpart 251.

The optical part 251 outputs the light from the sensor amplifier 400through the optical fiber 250 to the optical part 202 and guides thelight reflected at the shaft 91 output from the optical part 202 to theoptical fiber 250.

The sensor amplifier 400 is provided with a light emitting element 401and a light receiving element 402. The light emitting element 401 iscomprised of for example a laser diode. The light receiving element 402is comprised of for example a photo diode.

The sensor amplifier 400 outputs light to the optical fiber 250 by thelight emitting element 401 and receives the light reflected at the shaft91 input through the optical fiber 250 by the light receiving element402.

The light receiving element 402 converts the received light to anelectric signal in accordance with its intensity and outputs the signal402 s to the PLC 150.

The PLC 150 detects the rotational speed of the motor 80 based on thesignal 402 s from the sensor amplifier 400. Further, the PLC 150 outputsthe detected rotational speed of the motor 80 to the NC apparatus 250.Note that the PLC 150 is an embodiment of a rotational speed detectingmeans according to the present invention.

Next, an explanation will be made of an example of the operation of thetool 603 according to the present embodiment.

When the front end 85 a of the locking part 85 is inserted to and fitwith the fitting hole 47 a, the above optical part 202 faces the opticalpart 251.

Here, if the light emitting element 401 of the sensor amplifier 400outputs light, the light is input to the optical part 202 withoutcontact through the optical fiber 250 and the optical part 251. Thelight input to the optical part 202 is output from the optical part 201to the shaft 91 through the optical fiber 200.

When the spindle 46 is rotated at the rotational speed N₀ from thisstate, the tool attachment part of the tool 603 is rotated so that therotation of the spindle 46 is transmitted to the generator 70.

Due to this, for example a three-phase synchronous generator generatesthree-phase alternating current as the generator 70.

The motor 80 is driven by the three-phase alternating current suppliedfrom the generator 70.

While the shaft 91 of the motor 80 is rotating, when the reflectingmirror 125 arranged on the shaft 91 moves to a position facing to theoptical part 201, the reflecting mirror 125 reflects the light from theoptical part 201 to the optical part 201. Accordingly, a light signalhaving an intensity in accordance with the rotational speed of the shaft91 is input to the optical part 201.

The light signal having an intensity in accordance with the rotationalspeed of the shaft 91 is input to the light receiving element 402 of thesensor amplifier 400 through the optical fibers 200 and 250. The lightreceiving element 402 converts the light signal into an electric signaland outputs the electric signal 402 s to the PLC 150.

The PLC 150 detects the rotational speed of the motor 80 based on thesignal 402 s and outputs the detected rotational speed to the NCapparatus 250.

Due to this, the NC apparatus 250 can monitor the rotational speed ofthe motor 80 at all times. Further, the NC apparatus 250 can alsocontrol the rotation of the motor 80 indirectly by controlling therotation of the spindle 46 using the detected rotational speed of themotor 80.

According to the present embodiment, by arranging only the optical part,the optical fiber, and the reflecting mirror at the tool 603 side andarranging the light emitting element or the light receiving elementoutside of the tool 603, the rotational speed of the motor 80 built inthe tool 603 is detected. Due to this, it becomes possible to make thestructure of the tool 603 simple and compact and suitable for automatictool changing.

Note that in the above embodiment, the reflecting mirror 125 is mountedon the shaft 91, but it is also possible to mirror finish part of theshaft 91. Further, it is possible to arrange a plurality of reflectingmirrors 125 along the circumferential direction of the shaft 91.

Further, the method of detecting the rotational speed of the motor 80 isnot limited to the above method using the reflecting mirror 125. It ispossible to for example arrange a disk having a through hole on theshaft 91, output light from one side of the disk and receiving thepassed light at the other side of the disk, and generate a light signalin response to the rotational speed of the motor 80. That is, it ispossible to employ any configurations supplying light from outside ofthe tool 603, generating a light signal in accordance with therotational speed of the motor 80, and outputting this light signal tothe outside.

Fifth Embodiment

FIG. 9 is a front view of the configuration of another embodimentaccording to the present invention. Note that the same references areused for the same parts as in the above mentioned embodiments in FIG. 9.

As shown in FIG. 9, the tool 604 according to the present embodiment isprovided with a digital display 600 on the outer surface of the casing65. The digital display 600 displays the rotational speed of the motorbuilt in the tool 604.

FIG. 10 is a view of the configuration of the tool 604 according to thepresent embodiment.

The tool 604 according to the present embodiment has built into it thegenerator 70 and the motor 80 in the same way as the above tool 60according to the first embodiment. The rotation of the spindle 46 istransmitted to the generator 70 through the attachment part 62 so thatthe generator generates electric power. As the generator 70, athree-phase synchronous generator can be used.

The tool 604 according to the present embodiment is provided with arectifier circuit 302, an inverter 303, and a control circuit 304 inaddition to the generator 70 and the motor 80. The rectifier circuit302, the inverter 303, and the control circuit 304 are built in theabove casing 65.

The rectifier circuit 302 rectifies the alternating current generated bythe generator 70 and supplies it to the inverter 303.

Further, the rectifier circuit 302 supplies a part of the rectifieddirect current to the control circuit as a power supply.

The inverter 303 is an inverter for changing the direct current suppliedfrom the rectifier circuit 302 into alternating current having afrequency necessary for driving the motor 80. For example, the inverter303 is configured by a pulse width modulation (PWM) inverter.

The control circuit 304 is provided with a microprocessor 305, a readonly memory (ROM) 306, a random access memory (RAM) 307, a countercircuit 308, an analog-to-digital (A/D) converter 310, and adigital-to-analog (D/A) converter 309.

The ROM 306 stores a control program for controlling the motor 80. Thecontrol program performs for example variable speed control of the motor80 by field-oriented control.

The RAM 307 stores data for operations of the microprocessor 305.

The microprocessor 305 executes the control program stored in the ROM306, performs various operations, and outputs control signals 304 s tothe inverter 300 via the D/A converter 309. The control signals 304 sare for example PWM control signals.

Further, the microprocessor 305 detects the rotational speed of themotor 80 and outputs the rotational speed information Rn of the motor 80to the digital display 600.

The A/D converter 310 converts the value of the current supplied fromthe inverter 303 to the motor 80 detected by a current detector 312 intoa digital signal and outputs this signal to the microprocessor 305.

The motor 80 is provided with a rotational position detector 311. Asthis rotational position detector 311, for example, an optical rotaryencoder or a resolver may be used.

The counter circuit 308 counts pulse signals detected by the rotationalposition detector 311 in accordance with the rotation of the motor 80and outputs the count to the microprocessor 305.

The above configured control circuit 304 can operate by receivingelectric power generated by the generator 70 by the rotation of thespindle 46.

The control circuit 304 receives the rotation and the drive current ofthe motor 80 as input. Due to this, by preparing a desired controlprogram in the ROM 306 of the control circuit 304 in advance, varioustypes of control of the motor 80 becomes possible.

For example, when a synchronous motor is used as the motor 80 and it isintended to variably control the speed of this synchronous motor,velocity reference data is set in advance in the ROM 306. By this, speedcontrol of the motor 80 becomes possible in accordance with thisvelocity reference data.

Next, an explanation will be made of an example of the operation of theabove configured tool 604.

The alternating current generated by the generator 70 is rectified bythe rectifier circuit 302 and supplied to the control circuit 304 andthe inverter 303.

When electric power is supplied to the control circuit 304, the controlcircuit 304 starts to operate and executes a program stored in the ROM306. Due to this program, alternating current having a predeterminedfrequency is supplied from the inverter 303 to the motor 80, and themotor 80 is driven.

When the motor 80 is driven, a number of pulse signals in accordancewith the rotational speed of the motor 80 are input from the rotationposition detector 311 to the counter circuit 308. The counter circuit308 sequentially counts the number of the pulse signals and outputs thecount to the microprocessor 305.

The microprocessor 305 converts the rotational speed of the motor 80based on the count input from the counter circuit 308 and controls therotational position, the speed, the torque, etc. of the motor 80 usingthe rotational speed of the motor.

Further, the microprocessor 305 sequentially outputs the rotationalspeed information of the motor 80 to the digital display 600. By this,the present rotational speed of the motor 80 is displayed on the digitaldisplay 600.

In the present embodiment, the tool 604 is electrically independent ofthe spindle 46. Due to this, to obtain a grasp of the operational stateof the tool 604, it is necessary to employ a configuration transmittingthe information giving the operational state of the tool 604 to theoutside of the tool 604 with a wireless apparatus etc. By arranging thedigital display 600 on the casing 65, it becomes possible to easilyobtain a grasp of the operational state of the tool 604.

Note that in the present embodiment, the digital display 600 displaysthe rotational speed of the motor 80, but it is also possible to displayother information of the operational state of the motor 80 besides therotational speed, for example, the current supplied to the motor 80.Further, it is also possible to display a plurality of informationshowing the operational state of the motor 80.

Furthermore, it is also possible to detect not only the operationalstate of the motor 80 but also that of the generator 70 and display thisvisually recognizable from the outside.

While the invention has been described with reference to specificembodiments chosen for purpose of illustration, it should be apparentthat numerous modifications could be made thereto by those skilled inthe art without departing from the basic concept and scope of theinvention.

1. A machine tool comprising: a machine tool body provided with a spindle, a driving means for driving said spindle, and at least one control axis for changing a relative position between said spindle and a workpiece; a control apparatus for driving and controlling said driving means and control axis in accordance with a machining program; a tool attachable to said spindle and provided with a machining tool for machining a workpiece, a motor for driving said machining tool, a generator for generating electric power by the rotation of said spindle, a light signal generation means for generating a light signal in accordance with the rotational speed of said motor, and a light guiding means for guiding light into said light signal generation means from outside to output the light signal by said light signal generation means to the outside; a light receiving and emitting means for emitting light to said light guiding means without contact and receiving said light signal without contact; and a rotational speed detecting means for detecting the rotational speed of said motor based on said received light signal. 